1. Field of the Invention
The present invention relates to a fuel injector.
2. Background Information
FIG. 1 shows a fuel injector that is disclosed in U.S. Pat. No. 5,460,329 issued to Sturman. The Sturman injector includes an hydraulically-driven intensifier 1 that can pressurize a fuel located within a fuel chamber 2. The pressurized fuel is ejected through one or more nozzle openings 3 in a tip 4 of the injector. The flow of fuel through the openings 3 is controlled by a spring-biased needle or check valve 5.
The intensifier 1 has a head 6 that is located within an intensifier chamber 7. The intensifier chamber 7 is hydraulically coupled to a control valve 8 which can control the flow of an hydraulic fluid into the chamber 7. The control valve 8 is typically a three-way valve which can selectively hydraulically couple the chamber 7 to either a high pressure rail line (not shown) or low pressure drain line (not shown). When hydraulically coupled to the rail line, the high pressure hydraulic fluid flows into the intensifier chamber 7 and pushes the intensifier 1 into a downward or pumping direction. The downward movement of the intensifier 1 pressurizes the fuel within the fuel chamber 2. The pressurized fuel pushes the needle valve 5 into an (upward) open position so that fuel is ejected or sprayed through the nozzle openings 3.
The injector includes a return spring 9 which pushes the intensifier 1 back to its original (upward) position when the control valve 8 hydraulically couples the chamber 7 to the drain line. The upward movement of the intensifier 1 also draws fuel into the fuel chamber 2 so that the process can be repeated. The spring-biased needle valve 5 is also pushed back into its closed (downward) position.
The return spring 9 is located within a spring chamber 10. Hydraulic fluid within the intensifier chamber 7 may leak past the outer peripheral surface of the head 6 and into the spring chamber 10. Any fluid within the spring chamber 10 may create an hydrostatic pressure which impedes or prevents the downward movement of the intensifier 1. To prevent the build-up of hydrostatic pressure, the injector 1 may contain a drain passage 11 that is hydraulically coupled to the spring passage 10. The drain passage 11 allows hydraulic fluid which leaks into the spring chamber 10 to flow out of the injector. The drain passage 11 extends along the longitudinal axis of the injector to an outlet port 12 located adjacent to the control valve 8.
The fuel injector is typically assembled into an internal combustion engine. By way of example, the fuel injector may eject diesel fuel into a diesel engine. It is desirable to reduce the size of the fuel injector to minimize the overall size and weight of the engine. The existence of the longitudinal drain passage limits the minimum diameter or cross-sectional area of the fuel injector. In addition to the diameter or cross-sectional area of the drain passage, the passage also requires an outer wall which increases the size of the injector. It would be desirable to provide a fuel injector which does not have a longitudinal drain passage.